Transmission power control method and radio control apparatus in mobile packet communication system

ABSTRACT

A downlink user data signal destined for a specific mobile station ( 4 - 1 ) is always transmitted from a single base station while a plurality of base stations ( 3 - 1, 3 - 2, 3 - 3 , . . . ) being switched from one to another. A first downlink signal destined for the mobile station ( 4 - 1 ) is transmitted from one or a plurality of base stations through a first downlink radio channel (downlink A-DPCR). The transmission power of a second downlink radio channel (PDSCH, HS-SCCH) for transmitting a second downlink signal from the base station ( 3 - 1 ) to the mobile station ( 4 - 1 ) is provided with an offset relative to the transmission power of the first downlink radio channel from the base station ( 3 - 1 ) to the mobile station ( 4 - 1 ), thereby linking the transmission power of the second downlink radio channel with the transmission power of the first downlink radio channel. If the number of diversity branches, i.e., the number of base stations ( 3 - 1, 3 - 2 ) simultaneously communicating with the mobile station ( 4 - 1 ) on the first downlink radio channel (downlink A-DPCH) is large, the offset for the transmission power of the second downlink radio channel (PDSCH, HS-SCCH) is increased. If the number of diversity branches is small, the offset for the transmission power of the second downlink radio channel is decreased. In this way, the offset is determined. As a result, in mobile packet communication that transmits user data for a plurality of mobile stations through a single radio channel by temporally multiplexing the data, the reception quality of the second downlink signal transmitted from the specific base station ( 3 - 1 ) on the second downlink radio channel (PDSCH, HS-SCCH) can always properly be maintained.

TECHNICAL FIELD

The present invention relates to a transmission power controlling methodand a radio network control apparatus for a mobile packet communicationsystem.

BACKGROUND TECHNOLOGY

FIG. 1 shows a configuration of a standard mobile packet communicationsystem consisting of an exchange apparatus 1, a radio network controlapparatus 2, base stations 3-1, 3-2, 3-3, . . . controlled by the radionetwork control apparatus 2, and mobile stations 4-1, 4-2, . . .wirelessly communicating with one or a plurality of the base stationsand possessed by users, respectively.

TABLE 1 Correspondence between transport channels and physical channelsTransport Physical channel name channel name Official name DCH A-DPCHAssociated-Dedicated Physical Channel DCH DPCH Dedicated PhysicalChannel DSCH PDSCH Physical Downlink Shared Channel

This system achieves mobile packet communication by efficientlyutilizing frequencies and by considering a characteristic of packetcommunication that a certain extent of delay is allowable. FIG. 2 showsa communication technique usually employed by the system. The basestation 3 transmits data pieces D1, D2, and D3 to the user mobilestations 4-1, 4-2, and 4-3, respectively, by temporally multiplexing thedata pieces on a single radio channel PDSCH (Physical Downlink SharedCHannel).

This specification uses as a radio channel name a physical channel nameinstead of a transport channel name. Table 1 shows correspondencebetween transport channel names and physical channel names.

To allow a single radio channel to be shared by a plurality of users, aprior art employs a channel configuration shown in FIG. 3. Separatelyfrom a shared channel PDSCH for transmitting data (downlink user data)for user mobile stations, there are A-DPCHs (Associated-DedicatedPhysical CHannels) in an uplink and a downlink, respectively, to controltransmission power. The uplink also involves a physical channel DPCH(Dedicated Physical CHannel) to multiplex uplink user data and controlinformation sent from a mobile station.

According to the communication system of the prior art, the physicalchannel A-DPCH in the downlink only has a task of transmitting controlsignals, and therefore, is set at a relatively low channel speed. On theother hand, the physical channel DPCH in the uplink transmits controlsignals as well as user data, and therefore, is set at a channel speedhigher than the downlink physical channel A-DPCH. The shared channelPDSCH in the downlink is set at a channel speed that is further higherthan the downlink physical channel A-DPCH, to carryout high-speed datacommunication.

When conducting communication with the use of the high-speed sharedchannel PDSCH, a PDSCH transmission notice is sent to a mobile stationthrough the A-DPCH before transmitting data with a radio frame on thePDSCH. Upon receiving the notice, the mobile station confirms the PDSCHtransmission, and then, starts receiving the data on the PDSCH.

In this way, according to the conventional mobile packet communicationsystem, a base station notifies a plurality of mobile stations of sharedchannel PDSCH transmission through the downlink physical channel A-DPCH,and then, transmits user data through the PDSCH. Namely, user data for aplurality of users are transmitted to a plurality of mobile stations bytemporally multiplexing the data. In FIG. 3, the downlink involves twochannels, i.e., the physical channel A-DPCH and shared channel PDSCH.The PDSCH is not always set but is set only when notification is madethrough the A-DPCH.

Conventionally, the mobile packet communication mentioned above uses atechnique called diversity reception (hereinafter referred to as “DHO”)to improve the line quality of the physical channel A-DPCH and sharedchannel PDSCH in the downlink. FIG. 4 shows a channel configuration ofmobile packet communication employing the DHO technique. The basestations 3-1 and 3-2 simultaneously transmit signals through thedownlink physical channels A-DPCHs and receive the uplink physicalchannel DPCH from the mobile station 4-1. However, no DHO is applied tothe shared downlink channel PDSCH for transmitting user data becauseuser data of a plurality of users are temporally multiplexed, andtherefore, it is difficult to control data transmission timing in DHO.Accordingly, only one base station, e.g., the base station 3-1 uses thePDSCH for data transmission.

A code division multiple access (hereinafter referred to as “CDMA”)method is a radio communication technique employing codes to establish achannel. For such a technique, transmission power control is importantand essential, A W-CDMA system (Wideband Code Division Multiple Accesssystem) adopted by IMT-2000 employs a technique called high-speedtransmission power control. The high-speed transmission power controltechnique is applicable not only to the W-CDMA system but also to TDMAand FDMA Systems.

FIGS. 5 to 7 show an operation of transmission power control for CDMA.

In FIGS. 5 and 6, the mobile station 4-1:

(1) calculates a signal-power-to-interference-power ratio (hereinafterreferred to as “SIR”) of the downlink physical channels A-DPCH alwaystransmitted from the base stations 3-1 and 3-2;

(2) compares a result of the calculation with a predetermined targetvalue;

(3) if the comparison indicates that the calculated SIR is lower thanthe target value, generates a transmission power control command tocommand the base stations 3-1 and 3-2 to increase the transmission powerof the A-DPCH, and if the comparison indicates that the SIR is greaterthan the target value, generates a transmission power control command tocommand that the transmission power of radio signals for the mobilestation must be decreased; and

(4) transmits the generated transmission power control command to thebase stations 3-1 and 3-2 on the uplink physical channel A-DPCH.

In FIGS. 5 and 7, the base station 3-1:

(1) calculates a SIR of the uplink A-DPCH from the mobile station 4-1;

(2) compares the SIR of the A-DPCH with a predetermined target value,like the above-mentioned case of the mobile station;

(3) if the comparison indicates that the target value is lower than theSIR of the A-DPCH, generates a transmission power control command tocommand the mobile station 4-1 to increase the transmission power ofuplink radio signals, and if the comparison indicates that the SIR ofthe A-DPCH is greater than the target value, generates a transmissionpower control command to command that the transmission power of uplinkradio signals must be decreased; and

(4) transmits the generated transmission power control command to themobile station 4-1 on the downlink physical channel A-DPCH.

In this way, radio signal transmission power between the base station3-1 and the mobile station 4-1 is adjusted to always maintain optimumtransmission power.

On the other hand, the transmission power of the shared downlink channelPDSCH is controlled according to a value obtained by multiplying atransmission power value of the physical channel A-DPCH in the samedownlink by a predetermined value, i.e., an offset value. This isbecause the transmission power of the downlink A-DPCH is considered tobe always optimally controlled according to a transmission power controlcommand transmitted from a mobile station and because the A-DPCH andPDSCH are simultaneously transmitted. Accordingly, it is possible toconsider the A-DPCH and PDSCH are in the same radio channel state. Theoffset value is notified from the radio network control apparatus 2 toeach of the base stations 3-1, 3-2, and 3-3 in the mobile packetcommunication system of FIG. 9.

The conventional mobile packet communication system, however, will causea problem during diversity reception (DHO). This problem will beclarified with reference to FIG.

Each of the base stations 3-1 and 3-2:

(1) calculates, at each of the base stations 3-1 and 3-2, a SIR of theA-DPCH when receiving the uplink physical channel A-DPCH from a mobilestation;

(2) compares it with a target value;

(3) generates a transmission power control command to command atransmission power increase or decrease; and

(4) transmits, from each of the base stations, the transmission powercontrol command to the same mobile station through the downlink physicalchannel A-DPCH of the base station.

Accordingly, the mobile station receives the two transmission powercontrol commands.

On the other hand, the mobile station:

(1) receives the two A-DPCHs from the separate base stations, combinesthe two A-DPCHs according to a predetermined procedure, and calculates aSIR of the combined A-DPCHs;

(2) compares the SIR with a target value;

(3) generates, according to a comparison result, a transmission powercontrol command to command a transmission power increase or decrease;and

(4) transmits the transmission power control command on the uplinkphysical channel A-DPCH.

This A-DPCH is transmitted from the mobile station 4-1 simultaneously tothe base stations 3-1 and 3-2. This A-DPCH is a single radio signalalthough FIG. 8 shows two lines representative of the signal. Theseparate base stations 3-1 and 3-2 receive the same A-DPCH from themobile station 4-1.

According to the DHO technique, a mobile station receives signals from aplurality of base stations and combines the signals into one. As aresult, combined gains improve the quality of the downlink A-DPCHs.Similarly, a base station can receive a radio signal from a mobilestation at a plurality of locations and combine the received signalsinto one to improve the quality of A-DPCH.

When considering the downlink A-DPCHs during DHO, it is understood thatthe base stations 3-1 and 3-2 simultaneously transmit radio signals andthe mobile station 4-1 combines the signals together. Accordingly, thetransmission power of the downlink A-DPCH of each of the base stations3-1 and 3-2 can be small to realize the same SIR as that obtained whenno DHO is carried out (i.e., a single base station transmits thedownlink A-DPCH). More simply, transmitting a signal from two basestations instead of a single base station can halve the transmissionpower of each base station.

During DHO, the transmission power of the downlink physical channelA-DPCH of each of the base stations 3-1 and 3-2 is reduced. However, thetransmission power of the downlink shared channel PDSCH is calculated bymultiplying the downlink A-DPCH of the base station 3-1, which transmitsthe PDSCH, by an offset value without DHO. This results in deterioratingthe reception quality of the PDSCH during DHO.

The present invention has been made to overcome these conventionalproblems. An object of the present invention is to provide a techniqueof always maintaining good reception quality on a PDSCH during diversityreception in mobile packet communication that transmits user data for aplurality of mobile stations by temporally multiplexing the user data onthe single radio channel PDSCH.

Another object of the present invention is to provide a technique ofalways maintaining good reception quality on an HS-SCCH (High SpeedShared Control CHannel) of an HSDPA (High Speed Downlink Packet Access)method that fixes the transmission power of a data transmission channeland variably controls data quantities.

DISCLOSURE OF THE PRESENT INVENTION

An aspect of the present invention provides a transmission powercontrolling method for a mobile packet communication system. The methodincludes:

a step in which a mobile station checks a signal state of a firstdownlink radio channel from each of one or a plurality of base stationsfrom which the mobile station can receive signal radio waves, and basedon the signal state of the first downlink radio channel, transmits atransmission power control command to command a transmission powerincrease or decrease to each of the base stations through an uplinkradio channel paired with the first downlink radio channel;

a step in which each of one or a plurality of base stations specified bya radio network control apparatus to conduct communication with themobile station checks a signal state of the uplink radio channel fromthe mobile station, and based on the signal state of the uplink radiochannel, transmits a transmission power control command to command atransmission power increase or decrease through the first downlink radiochannel paired with the uplink radio channel;

a step in which the radio network control apparatus detects the numberof diversity branches of the mobile station communicating with the basestations, increases an offset if the detected number of diversitybranches is large, and decreases the offset if the number of diversitybranches is small, to thereby determine the offset;

a step in which the radio network control apparatus specifies, fromamong the one or plurality of base stations, a transmitter base stationto transmit signals to the mobile station through a second downlinkradio channel and notifies the transmitter base station to settransmission power of the second downlink radio channel to transmitsignals to the mobile station by multiplying transmission power of thefirst downlink radio channel by the offset; and

a step in which the transmitter base station to transmit signals to themobile station through the second downlink radio channel adjuststransmission power of the second downlink radio channel according to thenotification from the radio network control apparatus and transmitsdownlink signals transferred from the radio network control apparatus.

Another aspect of the present invention provides a transmission powercontrolling method for a radio network control apparatus in a mobilepacket communication system, including a step of making each of one or aplurality of base stations transmit a first downlink signal for aspecific mobile station through a first downlink radio channel, a stepof detecting the number of diversity branches of the mobile station,increasing an offset if the detected number of diversity branches islarge and decreasing the offset if the number of the diversity branchesis small, to thereby determine the offset, and a step of specifying,from among the one or plurality of base stations, a transmitter basestation to transmit a downlink signal to the mobile station through asecond downlink radio channel and notifying the transmitter base stationto set transmission power of the second downlink radio channel bymultiplying transmission power of the first downlink radio channel bythe offset.

Still another aspect of the present invention provides a radio networkcontrol apparatus having a diversity branch controller to control anincrease or a decrease in the number of diversity branches, a storageunit to store the number of diversity branches of each connected mobilestation, and an offset calculator to determine an offset value fortransmission power of a specific downlink radio channel for a givenmobile station according to the number of diversity branches of thegiven mobile station stored in the storage unit and notify a basestation concerned of the offset value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a standard mobile packet communicationsystem;

FIG. 2 is an explanatory view showing a scheme of time multiplexingtransmission on a PDSCH according to the standard mobile packetcommunication system;

FIG. 3 is an explanatory view showing signal channels for communicationbetween a base station and a mobile station according to a conventionalmobile packet communication system;

FIG. 4 is an explanatory view showing signal channels for communicationbetween a plurality of base stations and a mobile station according tothe conventional mobile packet communication system;

FIG. 5 is an explanatory view showing transmission power control usingA-DPCH and DPCH for communication between a base station and a mobilestation according to the conventional mobile packet communicationsystem;

FIG. 6 is a flowchart showing a process of generating a transmissionpower control command at a mobile station according to the conventionalmobile packet communication system;

FIG. 7 is a flowchart showing a process of generating a transmissionpower control command at a base station according to the conventionalmobile packet communication system;

FIG. 8 is an explanatory view showing a method of controllingtransmission power between two base stations and a mobile station in adiversity mode according to the conventional mobile packet communicationsystem;

FIG. 9 is a block diagram showing a functional configuration of a radionetwork control apparatus in a mobile packet communication systemaccording to a first embodiment of the present invention;

FIG. 10 is a flowchart showing a process executed by the above-mentionedradio network control apparatus;

FIG. 11 is an explanatory view showing signal channels for communicationbetween a base station and a mobile station according to a mobile packetcommunication system employing an HSDPA method;

FIG. 12 is a block diagram showing a functional configuration of a radionetwork control apparatus in a mobile packet communication systemaccording to a second embodiment of the present invention; and

FIG. 13 is a flowchart showing a process executed by the above-mentionedradio network control apparatus.

BEST MODE OF IMPLEMENTATION

The present invention will be explained with reference to theembodiments shown in the drawings. FIG. 9 shows a functionalconfiguration of a radio network control apparatus 2 in a mobile packetcommunication system according to an embodiment of the presentinvention. A hardware configuration of the mobile packet communicationsystem is the same as that of FIG. 1 explained in connection with theprior art. In this system, the embodiment of the present invention ischaracterized by the radio network control apparatus 2.

The mobile packet communication system shown in FIG. 1 consists of theexchange apparatus 1, radio network control apparatus 2, and basestations 3-1, 3-2, 3-3, . . . arranged in a step configuration. Themobile stations 4-1, 4-2, . . . that may be cellular phones possessed byusers, respectively communicate with the base stations through radiochannels.

The radio network control apparatus 2 centrally controls the basestations by specifying an offset value for a shared downlink channelPDSCH and by issuing instructions to add and remove DHO braches.

In FIG. 9, the radio network control apparatus 2 includes a user databuffer 21 to receive data from a trunk network and store the receiveddata, a queuing processor 22 to execute a queuing process, an offsetcalculator 23 to calculate an offset value to be explained later, a DHOcontroller 24 to control DHO branches, and a storage unit 25 to storenecessary data.

The user data buffer 21 of the radio network control apparatus 2receives through the trunk network user data bound for user mobilestations and temporarily stores the received data. The queuing processor22 controls a transmission sequence of data for the mobile stations andtransfers the user data stored in the user data buffer 21 to the mobilestations.

The offset calculator 23 calculates an offset value for a PDSCH of eachbase station related to a given user mobile station and issues a commandfor the offset value.

The DHO controller 24 responds to a branch add/delete request from amobile station and controls base stations to set branches according tothe request. After adding/deleting DHO branches, the DHO controller 24updates information related to the number of DHO branches of the usermobile station in question stored in the storage unit 25.

The storage unit 25 stores the number of DHO branches of each mobilestation and a data table of offset values corresponding to the numbersof branches of 1, 2, and 3.

A processing function of the offset calculator 23 will be explained withreference to the flowchart of FIG. 10. The offset calculator 23 receivesan ID notification for a transmission target mobile station from thequeuing processor 22 and retrieves the number of DHO branches related tothe user ID from the storage unit 25 (steps S1 and S2).

If the retrieved number of DHO branches is 1, the offset calculator 23issues a command to command a base station to use a normal offset valueA. If the number of DHO branches is 2, the offset calculator 23 notifiesthe base station of a value “A+B” obtained by adding B (dB) to theoffset A. If the number of DHO branches is 3, the offset calculator 23notifies the base station of a value “A+C” by adding C (dB) to theoffset A (step S3).

The offset adjusting values B and C may preferably be about 3 (dB) and 5(dB), respectively. This is because if the number of DHO branches is 2,it is assumed that the transmission power of a downlink physical channelA-DPCH has been halved, and therefore, about 3 (dB) will be appropriate.If the number of DHO branches is 3, the transmission power of the A-DPCHwill be about ⅓ of the value for the number of DHO branches of 1, andtherefore, 5 (dB) will be appropriate.

In this way, the mobile packet communication system according to theembodiment of the present invention changes an offset value applied tothe transmission power of a downlink shared channel PDSCH during adiversity (DHO) operation in response to the number of DHO branches. Theembodiment can substantially equalize the transmission power of a PDSCH,which is sent from a specific base station to a mobile station duringDHO, to a combined transmission power of A-DPCHs simultaneouslytransmitted from a plurality of base stations to the mobile station,thereby maintaining the quality of the PDSCH during DHO.

According to the embodiment mentioned above, the storage unit 25 of theradio network control apparatus 2 keeps the data table of offset valuescorresponding to the numbers of DHO branches, and the offset calculator23 retrieves an offset value corresponding to a given number of DHObranches from the storage unit 25. This does not limit the presentinvention. The offset calculator 23 may calculate an offset valueaccording to a functional operation expression f(x) where “x” is avariable representative of the number of DHO branches.

Next, a mobile packet communication system according to the secondembodiment of the present invention will be explained with reference toFIGS. 11 to 13. The present invention is applicable to an HSDPA (HighSpeed Downlink Packet Access) method, to control the transmission powerof an HS-SCCH (High Speed Shared Control CHannel) that is a controlsignal transmission channel.

The HSDPA method is a method shown in FIG. 11 having a channelconfiguration of (1) HS-PDSCH: a downlink data signal transmissionchannel; (2) HS-SCCH: a control signal transmission channel; and (3)downlink A-DPCH: a transmission power control dedicated channel anduplink A-DPCH: a data signal and control signal transmission channel.

For (1) HS-PDSCH, the method fixes the transmission power thereof andincreases or decreases a transmission data quantity thereof in responseto a signal state. For (2) HS-SCCH, the method variably controls thetransmission power thereof in response to a signal state. Controlsignals transmitted on the HS-SCCH include control information such as atransmission data size and a transmission originator in connection withpacket data sent on the HS-PDSCH.

The system of this embodiment employs the same hardware configuration asthat of the first embodiment shown in FIG. 1. The transmission power ofthe base stations 3-1, 3-2, . . . is controlled by the radio networkcontrol apparatus 2.

In FIG. 12, the radio network control apparatus 2 consists of a userdata buffer 21, a queuing processor 22, an offset calculator 230, a DHOcontroller 24, and a storage unit 25. This configuration issubstantially the same as that of the first embodiment shown in FIG. 9.The processing functions of the user data buffer 21, queuing processor22, DHO controller 24, and storage unit 25 are the same as those of thefirst embodiment.

The second embodiment is characterized by the offset calculator 230 thatcalculates, for each base station, an offset value applied to theHS-SCCH for a user mobile station concerned and issues a command for thecalculated offset value.

The processing function of the offset calculator 230 will be explainedwith reference to the flowchart of FIG. 13. Basically, the processingfunction is the same as that of the offset calculator 23 of the firstembodiment. Upon receiving a notification of an ID concerning atransmission target mobile station from the queuing processor 22, theoffset calculator 230 retrieves the number of DHO branches related tothe user ID from the storage unit 25 (steps S11 and S12).

If the retrieved number of DHO branches is 1, a command to use a normaloffset value A is issued to a base station, If the number of DHObranches is 2, a command to use a value “A+B” obtained by adding B (dB)to the offset is issued to the base station, and if the number of DHObranches is 3, a command to use a value “A+C” obtained by adding C (dB)to the offset is issued to the base station (step S13). The adjustingvalues for the offset are the same as those of the first embodiment.

In this way, the mobile packet communication system according to thisembodiment switches offset values for the transmission power of adownlink HS-SCCH from one to another during a diversity (DHO) operationin response to the number of DHO branches. Accordingly, the embodimentcan substantially equalize the transmission power of an HS-SCCH, whichis sent from a specific base station to a mobile station during DHO, toa combined transmission power of A-DPCHs simultaneously transmitted froma plurality of base stations to the mobile station, thereby maintainingthe quality of the HS-SCCH during DHO.

INDUSTRIAL APPLICABILITY

As mentioned above, the present invention controls each base stationthat relates to communication with a given mobile station in such a wayas to increase an offset for the transmission power of a second downlinkradio channel relative to the transmission power of a first downlinkradio channel if the number of diversity branches is large, and if thenumber of diversity branches is small, decrease the offset. Accordingly,the present invention can substantially equalize the transmission powerof a second downlink signal, which is sent from a specific base stationthrough the second downlink radio channel to the mobile station during adiversity operation, to a combined transmission power of the firstdownlink radio channels simultaneously transmitted from a plurality ofbase stations to the mobile station. Namely, the present invention cancontrol a specific base station to maintain the quality of the seconddownlink signal transmitted from the specific base station to a mobilestation during a diversity operation.

1. A transmission power controlling method for a mobile packetcommunication system involving a mobile station, a plurality of basestations, and a radio network control apparatus that controls the basestations to achieve radio packet communication between the mobilestation and one or a plurality of the base stations, the methodcomprising: a step in which the mobile station checks a signal state ofa first downlink radio channel from each of one or a plurality of thebase stations from which the mobile station can receive signal radiowaves, and based on the signal state of the first downlink radiochannel, transmits a transmission power control command to command atransmission power increase or decrease to each of the base stationsthrough an uplink radio channel paired with the first downlink radiochannel; a step in which each of the one or plurality of base stationsspecified by the radio network control apparatus to conductcommunication with the mobile station checks a signal state of theuplink radio channel from the mobile station, and based on the signalstate of the uplink radio channel, transmits a transmission powercontrol command to command a transmission power increase or decreasethrough the first downlink radio channel paired with the uplink radiochannel; a step in which the radio network control apparatus detects thenumber of diversity branches of the mobile station communicating withthe base stations, increases an offset if the detected number ofdiversity branches is larger than a predetermined number, and decreasesthe offset if the number of diversity branches is smaller than thepredetermined number, to thereby determine the offset; a step in whichthe radio network control apparatus specifies, from among the one orplurality of base stations, a transmitter base station to transmitsignals to the mobile station through a second downlink radio channeland notifies the transmitter base station to set transmission power ofthe second downlink radio channel to transmit signals to the mobilestation by multiplying transmission power of the first downlink radiochannel by the offset; and a step in which the transmitter base stationto transmit signals to the mobile station through the second downlinkradio channel adjusts transmission power of the second downlink radiochannel according to the notification from the radio network controlapparatus and transmits downlink signals transferred from the radionetwork control apparatus.
 2. The transmission power controlling methodof claim 1, wherein the mobile packet communication system employs aPDSCH, the first downlink radio channel is a downlink A-DPCH, the uplinkradio channel is an uplink A-DPCH, and the second downlink radio channelis the PDSCH.
 3. The transmission power controlling method of claim 1,wherein the mobile packet communication system employs an HS-PDSCH, thefirst downlink radio channel is a downlink A-DPCH, the uplink radiochannel is an uplink A-DPCH, and the second downlink radio channel is anHS-SCCH.
 4. A transmission power controlling method for a radio networkcontrol apparatus in a mobile packet communication system for providingmobile packet communication for a plurality of mobile stations,comprising: a step of making each of one or a plurality of base stationstransmit a first downlink signal for a specific mobile station through afirst downlink radio channel; a step of detecting the number ofdiversity branches of the mobile station communicating with the basestations, increasing an offset if the detected number of diversitybranches is larger than a predetermined number and decreasing the offsetif the number of the diversity branches is smaller than thepredetermined number, to thereby determine the offset; and a step ofspecifying, from among the one or plurality of base stations, atransmitter base station to transmit a downlink signal to the mobilestation through a second downlink radio channel and notifying thetransmitter base station to set transmission power of the seconddownlink radio channel by multiplying transmission power of the firstdownlink radio channel by the offset.
 5. The transmission powercontrolling method for a radio network control apparatus of claim 4,wherein the offset for transmission power of the second downlink radiochannel is an integer multiple of the number of diversity branches. 6.The transmission power controlling method for a radio network controlapparatus of claim 4, wherein the offset for transmission power of thesecond downlink radio channel is determined by selecting onecorresponding to the number of diversity branches from a data tableregistered in advance.
 7. The transmission power controlling method fora radio network control apparatus of any one of claims 4 to 6, whereinthe mobile packet communication system employs a PDSCH, the firstdownlink radio channel is a downlink A-DPCH, and the second downlinkradio channel is the PDSCH.
 8. The transmission power controlling methodfor a radio network control apparatus of any one of claims 4 to 6,wherein the mobile packet communication system employs an HS-PDSCH, thefirst downlink radio channel is a downlink A-DPCH, and the seconddownlink radio channel is an HS-SCCH.
 9. A radio network controlapparatus for controlling transmission power of a base station thatprovides mobile packet communication for a mobile station, comprising: adiversity branch controller to control an increase or a decrease in thenumber of diversity branches; a storage unit to store the number ofdiversity branches of each connected mobile station; and an offsetcalculator to determine an offset value for transmission power of aspecific downlink radio channel for the mobile station according to thenumber of diversity branches of the mobile station stored in the storageunit and notify the base station of the offset value.
 10. The radionetwork control apparatus of claim 9, wherein the offset calculatordetermines the offset for transmission power of the specific downlinkradio channel as an integer multiple of the number of diversitybranches.
 11. The radio network control apparatus of claim 9, whereinthe offset calculator determines the offset for transmission power ofthe specific downlink radio channel by selecting one corresponding tothe number of diversity branches from a data table registered in advancein the storage unit.
 12. The radio network control apparatus of any oneof claims 9 to 11, wherein the mobile packet communication employs aPDSCH and the offset for transmission power of the specific downlinkradio channel is an offset for transmission power of the PDSCH relativeto transmission power of a downlink A-DPCH.
 13. The radio networkcontrol apparatus of any one of claims 9 to 11, wherein the mobilepacket communication employs an HS-PDSCH and the offset for transmissionpower of the specific downlink radio channel is an offset fortransmission power of an HS-SCCH relative to transmission power of adownlink A-DPCH.